1. Field of the Invention
The present invention relates to selected ultra-violet light (UV) curable hot melt (or phase change) compositions that can be used either in a solid object printer such as a Thermojet printer to produce strong and desirable parts from CAD designs or in the adhesive industry to produce adhesive and their film coatings. In particular, this invention relates to UV curable phase change compositions which are comprised of (i) at least one UV curable urethane (meth)acrylate resin; (ii) at least one wax; (iii) at least one (meth)acrylate diluent; (iv) at least one photoinitiator; and (v) at least one polymerization inhibitor.
2. Brief Description of Art
Commercially available UV hot melt printers such as the 3D Thermojet solid object printer available from 3D Systems of Valencia, Calif., uses a phase change material or ink that is jetted through a print head as a liquid to form a wax-like thermopolymer part. These parts contain mixtures of various waxes and polymers and are solid at ambient temperatures, but convert to a liquid phase at elevated jetting temperatures. Accordingly, such phase change materials used in such printers are required to have a melting point of at least 65° C. and a viscosity of about 13 cPs at about 130° C. to about 140° C. (jetting temperature). Suitable waxes useful in these jettable phase change materials have included paraffin, microcrystalline waxes, polyethylene waxes, ester waxes and fatty amide waxes. Suitable polymers useful for these phase change materials have included polyurethane resins, tall oil rosin and rosin ester polymers.
Existing phase change materials have some problems associated either with their physical characteristics (e.g. they are weak and brittle and subject to cracking after being jetted) or have processing limitations (e.g. they must be jetted at relatively high temperatures (130-140° C.)) because of the high viscosities of the individual components of such materials. Accordingly, there is a need for better materials that overcome these problems. The present invention is believed to solve these problems.
This patent application is related to U.S. application Ser. No. 09/924,608 filed Aug. 6, 2001, which is a continuation of prior U.S. application Ser. No. 09/252,512, filed Feb. 18, 1999, now U.S. Pat. No. 6,270,335, which is a divisional of U.S. application Ser. No. 08/722,335, filed Sep. 27, 1996, now abandoned, which is a continuation-in-part of U.S. application Ser. No. 08/534,813, filed Sep. 27, 1995, now abandoned. This application also relates to U.S. Pat. No. 6,193,923 (Ser. No. 09/252,512) which issued on Feb. 27, 2001 and is a divisional of Ser. No. 08/722,335. All of these related applications are incorporated by reference in their entirety herein